A method using biological information, such as an electrocardiogram or brain wave, is known for a general technique for measuring a mental burden (stress) of a subject. The method using biological information requires regulated conditions to a test subject in many cases and needs a relatively long time to analyze the data. For this reason, the method is used for judging stress of a subject in a resting condition.
A person frequently suffers from large stress when he/she drives a vehicle etc. (stress at work). A situation where the person suffers from the stress and a level of the stress vary from person to person. For example, in a situation where vehicle ride is uncomfortable or steering performance is poor, excessive strain is apt to occur in the person. Such excess strain is likely to hinder a smooth driving, possibly causing an accident.
In development and design for a vehicle etc., an electromyogram, which is easily measured and high in responsivity among biological information, is obtained from myoelectric potential signals indicating activities of the muscles of parts of the human body whose loads are large during driving, such as the arms and the feet, and a burden of the test subject at driving is directly judged.
Generally, when a human being suffers from a mental burden from stress, “strain” as unintentional excessive muscle activity generally appears. Accordingly, such a mental stress can be measured by measuring an activity state of the muscle.
Muscle activities of the arms and the feet, which are largely engaged in work such as driving of a vehicle, are measured in the form of an electromyogram, movement of the muscles at work is measured, and a physical burden of a human body is judged in conventional cases. However, a mental burden (stress) at work cannot be objectively expressed on the basis of this electromyogram.
For example, in the electromyogram describing the activities of the muscles at work such as the arm and the foot, a myoelectric potential signal representing the muscle activities by work such as driving of a vehicle and a myoelectric potential signal representing the muscle “excessive strain” due to the stress are superposed on each other. It is thus difficult to discriminate the muscle activity by the stress from the muscle activity of driving.
The method using biological information other than the electromyogram often requires regulations of a test subject and needs a relatively long recording time to analyze the data. Therefore, it is difficult to correctly evaluate stress at work.
In conventional development and design for a vehicle etc., items relating to the mental burden (stress), such as riding comfort and steering performance, are merely described in terms of a test subject feeling that is subjectively judged in words. As a result, it is impossible to objectively judge the stress.
The present invention has been made in view of the above, and has an object to provide a stress-at-work judging apparatus which can objectively judge stress at work by quantitatively measuring the “strain” that is generated from stress at work such as driving of a vehicle, a stress-at-work judging program and a stress-at-work judging method.